DE3932006A1 - METHOD FOR APPLYING PHOSPHATE - Google Patents

Description

The invention relates to a method for applying Phosphate coatings on metal surfaces with the help of Phosphating solutions based on zinc phosphate, the additionally contain nickel and formic acid, as well as its Use in diving to produce phosphate coatings Steel, galvanized steel and / or alloy galvanized steel, especially as preparation of the metal surfaces for the Electro dip painting.

It is known to coat phosphate on steel surfaces, galvanized steel or alloy galvanized steel with the help of phosphating solutions to produce the Belong to zinc / nickel phosphate system. If the too treating surfaces made of so-called composite metals, such as steel and galvanized steel and / or galvanized alloy Steel, the use of Phosphating solutions of the Zinc / nickel / manganese phosphate system introduced. The after phosphate coatings produced by these processes increase the Corrosion resistance of the treated metal surfaces and the liability of a subsequently applied paint, especially if the paint is electrocoated is applied.

The effect of nickel in the aforementioned In particular, phosphating systems consist of: Corrosion resistance after subsequent painting to increase that of manganese, to improve for that cationic electrocoating required Increase alkali resistance. The presence of manganese also helps improve the so-called Wet grip at.  

The aforementioned phosphating systems contain zinc and nickel or zinc, nickel and manganese, accelerators, the in particular nitrate ions, chlorate ions, nitrite ions and / or Can be nitrobenzenesulfonic acid. The application of the Phosphating solutions are generally used for Temperatures in the range of 30 to 60 ° C, where Dip process, spray process or combined Immersion spraying processes are common.

Based on the knowledge that an increased nickel content in the Phosphate coating especially the corrosion resistance phosphated and painted metal surfaces increased one tries to increase the nickel content in the Phosphating solution to increase the nickel content in the layer increase. High concentrations of nickel ions in the However, phosphating solutions are expensive connected. Furthermore, it has been shown that at simultaneous presence of manganese ions in the nickel content Phosphate coating did not increase to the extent expected can be. For a certain proportion of manganese ions in the phosphating solution is reluctant to do without, however otherwise the alkali resistance and wet grip of the generated phosphate coating decrease.

The object of the invention is to provide a phosphating process To provide treatment of metal surfaces that too High quality phosphate coatings, especially high ones Corrosion resistance results, and for excellent Wet adhesion of the lacquer film subsequently applied is responsible, and yet in a simple way is feasible.

The task is solved by the procedure of the beginning mentioned type designed in accordance with the invention is that the metal surfaces with a Phosphating solution in contact that 0.3 to 5 g / l Formic acid (calc. As HCOO) contains.  

Surprisingly, it has been shown that the aforementioned content of the phosphating solution Formic acid even at comparatively low Nickel concentrations of phosphate coatings with relatively high Nickel shares can be obtained.

The formic acid or formate content can can be brought about by using the phosphating solution Formic acid as such or salts of formic acid, such as alkali formate, alkaline earth formate, ammonium formate or Heavy metal formates added. Particularly suitable Compounds are sodium formate, potassium formate, Calcium formate, barium formate, ammonium formate, Nickel formate, cobalt formate, iron (III) formate and Manganese formate. The concentrations range from 0.3 to 5 g / l are important insofar as they are added the effect corresponding to a concentration <0.3 g / l with regard to the deposition of nickel ions on the treating metal surface is inadequate, whereas with addition of more than 5 g / l an increase in the effect is practically no longer available. Particularly advantageous is to add formic acid or formate measured that a concentration of 1.0 to 3.0 g / l results.

A preferred embodiment of the invention provides for the metal surfaces to be brought into contact with a phosphating solution which contains 0.5 to 2 g / l of zinc. At zinc concentrations of less than 0.5 g / l, a uniform phosphate coating is practically no longer possible, whereas at concentrations above 2 g / l, the proportion of hopeit (Zn ₃ (PO ₄ ) ₂ × 4H ₂ O) in the phosphate coating increases and thus its suitability as a primer for a subsequent electro-dip coating decreases. Particularly favorable results are achieved if the zinc content in the phosphating solution is 0.7 to 1.5 g / l.

According to a further expedient embodiment of the Invention should use the metal surfaces Phosphating solution are brought into contact, the 0.5 contain up to 3.0 g / l nickel. At a concentration of less than 0.5 g / l there is a risk that despite the presence the reducing formic acid or the reducing acting formate the deposited amount of nickel is insufficient, so that the corrosion resistance achieved the phosphate coating and its adhesion a subsequently applied lacquer film is not the optimum to reach. When a concentration of 3 g / l is exceeded is an additional increase in the quality of the produced No longer reach phosphate coating. Usually is a concentration of 2 g / l nickel is perfect sufficient.

The addition of manganese ions, especially in the case of partial galvanized or alloy galvanized steel for an increase the alkali resistance of the phosphate coating and the Wet adhesion of the subsequently applied paint is responsible should correspond to another advantageous embodiment of the invention in the range of 0.3 up to 1.5 g / l. If the concentration is higher than 1.5 g / l, the properties of the Phosphate coating especially with regard to Deteriorate corrosion resistance. Usually it is sufficient if the manganese content of the phosphating solution Is 1 g / l. At concentrations of the manganese ions below 0.3 g / l is the desired effect in the required Extent no longer achievable.

Further advantageous refinements of the invention consist in bringing the metal surfaces into contact with a phosphating solution which contains 10 to 25 g / l phosphate (calc. As PO ₄ ) or 0.5 to 2.0 g / l simple and / or complex Fluoride (calc. As F) contains. The fluoride ions can be introduced into the solution as hydrofluoric acid or as complex fluorides, for example in the form of fluorosilicate or fluoroborate. The addition of fluorides serves in particular to rapidly form the phosphate coating even at low temperatures, to refine the phosphate crystals and to increase the phosphophyllite content (Zn ₂ Fe (PO ₄ ) ₂ × 4H ₂ O) in the phosphate coating when treating steel surfaces. If the fluoride content is less than 0.5 g / l, the effect achieved may be too low, while at concentrations above 2.0 g / l an additional improvement in the effect can no longer be achieved.

The one used in the method according to the invention Usually contains phosphating solution Oxidizing agents that accelerate coating formation. According to a further advantageous development are used as accelerators nitrate, chlorate, nitrite and / or Nitrobenzenesulfonate ions individually or in any Combination used. The concentrations should in terms of nitrate ions 2 to 15 g / l, in terms of Chlorate ions 0.1 to 1 g / l, in terms of nitrite ions 0.01 to 0.2 g / l and in terms of Nitrobenzenesulfonate ions amount to 0.3 to 2.0 g / l. At Concentrations of the accelerators below the specified The lower limit is the acceleration effect achieved usually not sufficient while at concentrations an additional accelerating above the upper limit Effect can no longer be achieved or as a result of Otherwise disadvantageous entry in the phosphate layer Effects can occur.

The inventive method is in the usual Process of producing phosphate coatings integrated by the metal surfaces to be treated first a thorough cleaning, then one Activation, for example with colloidal titanium phosphate, and then subjected to the phosphating treatment  will. The phosphating treatment is expediently carried out at a temperature in the range of 20 and 55 ° C for the Duration from 30 to 180 sec.

According to a preferred embodiment of the invention the method according to the invention is used in Diving.

The process is particularly advantageous in terms of generation of phosphate coatings on steel, galvanized steel and / or alloy galvanized steel applicable. The galvanizing can both electrolytically and through Hot-dip galvanizing takes place. Particularly suitable zinc alloys are zinc-nickel and zinc-iron alloys. The too Treating metal surfaces can be in the form of sheet metal or Band, but also as already deformed workpieces, for example as automobile bodies. The The inventive method is particularly suitable for Preparation of metal surfaces for the subsequent Painting, the electro-dip painting and here the cathodic electrocoating plays a special role play.

The advantage of the method according to the invention is that that in the phosphating solution nickel in considerable amounts on the surface of the to be treated Workpiece is deposited and this nickel as Crystallization germ for the phosphate formation works. The The consequence is that very fine-grained phosphate coatings are formed, which also contains a significant amount of nickel in the Contain phosphate layer itself. Furthermore, the Rate of oxidation in the treatment of dissolved iron (II) ions to iron surfaces Iron (III) ions are reduced with the result that a considerable phosphophyllite content in the phosphate coating is installed.  

The phosphate coatings produced show

• (a) when treating steel surfaces
  Zn₂Fe (PO₄) ₂ · 4 H₂O
  as a main component and as a secondary component
  Zn₂Ni (PO₄) ₂ · 4 H₂O,
  if necessary also
  Zn₂Mn (PO₄) ₂ · 4 H₂O and small amounts
  Zn₃ (PO₄) ₂ · 4 H₂O
  as well as microns of Ni,
• (b) when treating zinc surfaces
  Zn₃ (PO₄) ₂ · 4 H₂O
  as a main component and as a secondary component
  Zn₂Ni (PO₄) ₂ · 4 H₂O,
  if necessary also
  Zn₂Mn (PO₄) ₂ · 4 H₂O,
  if Fe ^{2+ is} present in the treatment ^solution :
  Zn₂Fe (PO₄) ₂ · 4 H₂O, and Ni

on.

The invention is illustrated by the following examples and explained for example.

Examples

There were three different metal surfaces treated. This was it

• - for steel sheet samples according to SPCC according to JIS-G-3141 (hereinafter referred to as the SPC),
• - around electrolytically galvanized sheet steel (hereinafter referred to as the EC),
• - hot-dip galvanized sheet steel (hereinafter referred to as GA).

The respective metal surfaces were treated after the following procedure

• a) Degrease with a strong alkaline cleaner 40 ± 2 ° C in diving, for 180 sec.
• b) Rinse water by spraying for 20 sec Tap water at room temperature.
• c) conditioning the surface by treating with a titanium-containing activating agents (Preparen ZN) in Diving for 30 seconds at room temperature and one Concentration of the activating agent of 1 g / l.
• d) phosphating by dipping for 120 seconds; the applied in each case Phosphating solutions are in the following Table defined in more detail.
• e) water rinsing 20 sec, spraying with tap water from Room temperature.  
• f) Rinse with deionized water in the syringe for the Duration of 20 sec.
• g) drying at 110 ° C for 180 sec.

The determination of the free acid given in the table (F.A.) was carried out by titrating a 10 ml bath solution with 0.1 n-NaOH against bromophenol blue as an indicator. The one here The required number of ml 0.1 n-NaOH corresponds to the number of points Free acid.

The total acidity (T.A.) was determined by Titrate a 10 ml bath sample with 0.1N NaOH against Phenolphthalein as an indicator up to the discoloration of colorless to pink. Here, too, is the consumption of ml 0.1 n-NaOH equal to the number of points.

Following the phosphating, the individual Samples with a cathodic electrocoat (Elecron 9400, manufacturer Kansai Paint Co. Ltd.) at a Bath temperature of 28 ° C and applying a voltage of 250 V for a period of 180 sec. The thickness of the Paint layer was 20 microns.

Following the electrodeposition coating was initially 20 sec with tap water and then 5 sec with deionized water is rinsed at room temperature. Then the paint layer was baked at 175 ° C during 30 min.

After applying the base coat, a Melamine alkyd paint (Amilacque N-2 from Kansai Paint Co. Ltd.) applied as a filler in syringes. After a 10th it was baked in for up to 20 minutes 140 ° C for 30 min. The thickness of the paint layer created was 30 µm.  

Finally, using a melamine alkyd varnish (Amilacque WHITE M-3 from Kansai Paint Co. Ltd.) im Spray the top coat applied. Also followed here 10 to 20 minutes to dry the bake for the duration of 30 min at 140 ° C. The layer thickness when dry was 40 µm.

The painting treatment resulted in one Total layer thickness of 90 µm.

The sheets treated in this way were then subjected to various tests. First, the Evaluation of the quality of the phosphate coating.

• (a) Appearance of the coating:
  o - fine and even phosphate coating
  x - poor coating formation, especially inhomogeneous coating
• (b) Coating weight:
  • (ba) The coating was removed from SPC with an aqueous solution of 50 g / l chromic anhydride and the coating weight was calculated from the weights before and after the removal.
    Unit: g / m²
  • (bb) coated steel sheet (electrolytic or hot-dip galvanized):
    The coating was removed with an aqueous solution which contained 20 g / l ammonium bichromate and 480 g / l 29% ammonia, and the layer weight was determined from the weights of the samples before and after the removal.
    Unit: g / m²
• (c) Alkali resistance of the coating:
  The phosphated steel sheet was immersed in 0.1N NaOH at 30 ° C for 5 minutes. The amounts of phosphorus before and after immersion were measured and compared with an X-ray fluorescence analyzer. The alkali resistance was evaluated in each case from three test pieces according to the formula

Further tests were carried out

• a) to determine the on the treated metal surface adhering amount of nickel and possibly manganese with the help the X-ray fluorescence method. The measured values are in the Table given mg / m².
• b) To determine the adhesive strength of the Phosphating treatment applied paint.

To determine the resistance to hotter The painted sheet metal samples were initially saline scratched to the metal surface and then in a 5% saline solution of 240 h 55 ° C submerged. Then the incision was made Adhesive tape applied and torn off and the width the paint removal from the scratch point. Unit: mm In another test, the painted sheets were Immersed in demineralized water at 40 ° C for 240 h. The Sheet was then cut with a cross-cut in the manner provide that 100 fields with a field size of 1 × 1 mm was created. By pressing and pulling one Adhesive tape was the number of on the Metal surface remaining fields determined.  

The table below shows that the process according to the invention is used to produce phosphate coatings of a fine, uniform quality which have excellent alkali resistance and therefore have only an extremely minor impairment in cathodic electrocoating. It can also be seen that the corrosion resistance after painting and the adhesion of the paint layer are excellent.

Claims (10)

1. Process for applying phosphate coatings on metal surfaces with the aid of phosphating solutions based on zinc phosphate, which additionally contain nickel and formic acid, characterized in that the metal surfaces are brought into contact with a phosphating solution which contains 0.3 to 5 g / l, preferably 1 up to 3 g / l, formic acid (calc. as HCOO) contains. 2. The method according to claim 1, characterized in that one with a metal surface Phosphating solution in contact that 0.5 to Contains 2 g / l, preferably 0.7 to 1.5 g / l, of zinc. 3. The method according to claim 1 or 2, characterized characterized in that the metal surfaces with a Phosphating solution in contact that 0.5 to Contains 3 g / l nickel. 4. The method according to claim 1, 2 or 3, characterized characterized in that the metal surfaces with a Phosphating solution in contact that 0.3 to 1.5 g / l, preferably 0.3 to 1.0 g / l, contains manganese. 5. The method according to one or more of claims 1 to 4, characterized in that the metal surfaces are brought into contact with a phosphating solution which contains 10 to 25 g / l phosphate (calculated as PO ₄ ). 6. The method according to one or more of claims 1 to 5, characterized in that the metal surfaces in contact with a phosphating solution that 0.5 to 2.0 g / l simple and / or complex fluoride (calculated as F) contains. 7. The method according to one or more of claims 1 to 6, characterized in that the metal surfaces are brought into contact with a phosphating solution which
2 to 15 g / l NO₃ ions
0.1 to 1.0 g / l ClO₃ ions
0.01 to 0.2 g / l NO₂ ions
0.3 to 2.0 g / l nitrobenzenesulfonate ions
contains individually or in any combination. 8. Application of the method according to one or more of the Claims 1 to 7 in diving. 9. Application of the method according to one or more of the Claims 1 to 7 on the generation of Phosphate coatings on steel, galvanized steel and / or alloy galvanized steel. 10. Application of the method according to one or more of the Claims 1 to 7 on the preparation of Metal surfaces for electrocoating, especially cathodic electrocoating.